Novel dye removing agent based on CTS-g-P(AA-co-NIPAM)/GO composite

Kyohairwe Angela Mwesigye; Bin Zhou; Fangyuan Wang; Linhui Zhu; Yaoji Tang

doi:10.1016/j.arabjc.2023.104581

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Original article

04 2023

:16;

104581

doi:

10.1016/j.arabjc.2023.104581

Novel dye removing agent based on CTS-g-P(AA-co-NIPAM)/GO composite

Kyohairwe Angela Mwesigye, Bin Zhou, Fangyuan Wang, Linhui Zhu^⁎, Yaoji Tang^⁎

College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, PR China

⁎Corresponding authors. zhulinhui@yeah.net (Linhui Zhu), yjtang@sdust.edu.cn (Yaoji Tang)

Received: 2022-9-11, Accepted: 2023-1-10,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

A novel composite Chitosan graft poly (acrylic acid-co-N-isopropylacrylamide)/graphite oxide (CTS-g-P(AA-co-NIPAM/GO) is synthesized and used to remove methylene blue (MB) and fuchsin basic (FB) from aqueous solutions by adsorption. Small amount of GO brings about great improvement of the thermostability together with the adsorption amount. Adsorption capacities of MB and FB increase from 842.1 and 633.7 mg/g, respectively, to 1496.3 and 1000.8 mg/g, respectively, with 0.02 g intercalation amount of GO. The interactions between GO and main body of CTS-g-P(AA-co-NIPAM) graft copolymer are hydrogen and amide bonds, whereas that between dye molecules and CTS-g-P(AA-co-NIPAM)/GO composite is hydrogen bond as well as electrostatic interaction. Effect of various conditions on the adsorption capacities is discussed. Adsorption isotherms and thermodynamics are studied. The adsorption of both MB and FB are spontaneous and satisfy the Redlich-Peterson equation. Kinetic study shows that the adsorption of both dyes is in accordance with the Pseudo first-order kinetic model.

Keywords

Graphite oxide

Composite

Adsorption

Dyes

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1 Introduction

Nowadays, the waste dyes in the printing and dyeing industry has become one of the main causes of water pollution. As a fact that dyes can absorb light thereby reduce the transparency of water, the growth of aquatic organisms and microorganisms is influenced hence human health is threatened greatly. Although it is urgent to deal with the waste dyes especially those with high toxicity and chromaticity in water, to treat dye wastewaters seems to be a thorny problem because of the high solubility and complex molecular structure of dyes (Dadfarnia et al., 2015; Zhang et al., 2014).

Methylene blue (MB) is one of the most representative cationic dyes which is discharged after dyeing of cotton, wool, silk and paper, etc (Calimli et al., 2020). Despite its low toxicity MB is concerned to be associated with several diseases and discomfort such as eye burns, nausea, vomiting, diarrhea, dyspnea and tachycardia (Siciliano et al., 2021).

Basic fuchsin (BF) is a triaminotriphenylmethane dye which is widely used as coloring agent for textile and leather materials. It is also used to stain collagen, muscle, mitochondria, and tubercle bacillus (Luna, 1968). Contact with FB may cause severe eye and skin irritation. Inhalation or ingestion may cause damage to the organs such as blood, liver, spleen, and thyroid. Repeated exposure to the dye may affect the nervous system with headache, dizziness, lethargy, and muscle contraction. Therefore, on this point of view, it is urgent to develop effective methods for the removal of MB and FB from polluting effluents and contaminated water so as to allow a sustainable management of aquatic resources and prevent risks for human health (Gupta et al., 2008).

Recently various methods have been tried to remove dyes from wastewaters, including biological treatment (Pandey et al., 2007), membrane separation (Damodar et al., 2010), flocculation (Choi, 2015), visible light-induced degradation (Saravanan et al., 2016), adsorption (Zhu et al., 2012; Gupta and Saleh, 2013; Tang et al., 2018; Fallah et al., 2020; Iqbal et al., 2022 ), etc. Among them, adsorption is confirmed to be the most effective and economic one for it is selective, cost-effective, relatively simpler and easy to operate (Zhou et al., 2019). Many adsorbents are used to deal with dye wastewaters. It is reported that commercial activated carbons are efficient to reduce the organic load in secondary or tertiary treatment without by-products. However, they are quite expensive and nonselective (Crini et al., 2019). The alternative non-conventional green adsorbents such as biomasses are inexpensive but the adsorption processes using these materials are basically at the laboratory stage (Crini et al., 2010). Clay minerals such as bentonite, kaolinite, and diatomite demonstrate a strong affinity for dyes. Nevertheless, the adsorption ability for acid dyes is poor due to the ionic charges on the dyes and clay characters (Badawi et al., 2021). Therefore, it is urgent to find new adsorbent with low cost but high efficiency to deal with various dyes in wastewaters.

Superabsorbent resins (SAR) are a series of polymeric materials with strong hydrophilic groups such as hydroxyl, carboxyl and acylamino groups. They have not only excellent water absorption and retention properties but good adsorption capacities since the small molecules such as water and dye molecules are capable of being captured by SAR through chemical or electrostatic interaction. Thus, great attention has been paid to the preparation and application of SAR in recent years. A cellulose-g-poly(acrylic acid) resin with an excellent swelling capacity of 1900 g/g in distilled water was synthesized (Thien et al., 2022). A pH sensitive nanocomposite hydrogel based on katira gum-cl-poly(acrylic acid-co-N, N-dimethylacrylamide) incorporated bentonite (BT) (KGNCH) was also prepared (Jana et al., 2019). The adsorption of cationic dyes onto the hydrogel was found to be pH dependent, the adsorption isotherms and kinetics were fitted with the Freundlich isotherm and pseudo second order kinetic model, respectively. However, the large-scale applications of SAR are restricted because of the poor biodegradation and reuse performances of it.

N-isopropylacrylamide (NIPAM) is one of the acrylamide derivatives which is nontoxic, highly water-soluble and biocompatible (Boddu et al., 2019; Soleimani et al., 2013; Ma et al., 2019 ). A series of copolymers with NIPAM and methacrylic acid (Kametani et al., 2018; Martinez-Moro et al., 2020); polyacrylic acid (Kozhunova et al., 2022) and graft copolymers onto styrene butadiene rubber (Hermann et al., 2014); cellulose (Kumar et al., 2019); chitosan (Ifuku et al., 2013; Wang et al., 2016), alginate (Liu et al., 2019) were synthesized. It showed that polymers based on NIPAM are highly effective to remove organic dyes from aqueous solutions (Parasuraman et al., 2013). Since NIPAM is a temperature sensitive monomer, the preparation method of SAR based on NIPAM and its derivatives is of great importance.

Graphite oxide (GO) is a new kind of carbon nano-material which has high hydrophilic and good dispersive properties. It also has excellent thermodynamic properties and electrical performances. In recent years GO has been used to improve the thermostability, electric property, mechanical property, water absorption as well as the adsorption behavior of the products (Abu-Nada et al., 2021). A porous xylan/poly(acrylic acid)/graphite oxide nanocomposite was prepared by graft polymerization and used for adsorption of cationic ethyl violet in wastewaters (Fu et al., 2019). It showed that this material had excellent adsorption properties for ethyl violet (273.99 mg/g). A novel composite material consisted of cross-linked chitosan and GO was also synthesized and used to remove reactive Black 5 in aqueous solutions (da Silva et al., 2021). Similar work has also been accomplished by our research group in the past few years (Zhu et al., 2017; Tang et al., 2020).

In this article, chitosan graft poly (acrylic acid-co- N-isopropylacrylamide)/graphite oxide (CTS-g-P(AA-co-NIPAM/GO) composite hydrogel is synthesized by solution intercalation polymerization using potassium persulphate (KPS) as an initiator and N,N’-methylene bisacrylamine (MBA) as a cross-linker. The composite is characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The composite is used to remove methylene blue (MB) and fuchsin basic (FB) from aqueous solutions through adsorption at room temperature. The effect of GO on the thermo-stability and adsorption properties of the composite is studied. Effect of other conditions, including the initial concentration of dye solutions, contact time, ionic strength and dosage of the composite, on the adsorption capacities is also discussed in detail. Formation and adsorption mechanisms are speculated. The adsorption isotherms, thermodynamics together with the kinetics are discussed.

2 Experimental

2.1

2.1 Materials

The graphite (10000 mesh) is from Jin Rilai graphite Co.ltd., Qingdao, Shandong. Sodium nitrate (GR, 98.5 %), pertassium permanganate (AR, 99 %) and hydrogen peroxide solution (30 %) are all from Tianjin Kemiou Chemical reagents Co., ltd. Methylene blue (MB, AR, 99.9 %) and fuchsin basic (FB, AR, ≥99 %) are both from Tianjin Bodi Chemical Co., ltd., Tianjin, China. The properties and chemical structures of them are shown in Table 1. Chitosan (CTS, biological reagent, 99 %, the deacetylation degree 90 %, the molar weight 161 g/mol) is from Shandong Xiya Chemical Industry, Linyi, China. The monomers acrylic acid (AA, CP, ≥99 %) and N-isopropylacrylamide (NIPAM, biological reagent, ≥98 %) are both from Tianjin Kemiou Chemical Reagent Corporation ltd., Tianjin, China. The cross-linker N,N’-methylenebisacrylamide (MBA, AR, ≥99 %) and the initiator potassium persulfate (KPS, AR, ≥99 %) are both from Chengdu Kelong Chemical Reagent Factory, Chengdu, China. All the reagents are used directly without further purification.

2.2

2.2 Preparation

2.2.1

2.2.1 Preparation of GO

GO is prepared according to the modified Hummers method as stated in the literature (Hummers and Offema, 1958). The GO dispersion (0.002 g/mL) is prepared by dispersing 2 g of dry GO powder into 1000 mL of distilled water (Zhu et al., 2018).

2.2.2

2.2.2 Preparation of CTS-g-P(AA-co-NIPAM) /GO

A partially neutralized AA solution (neutralization degree 80 %) was prepared by stirring the mixture of AA (7.2 g) and sodium hydroxide solution (25 wt%, 12.8 g) in a beaker for 20 min in an ice-water bath. The neutralized AA solution was poured into a three-necked flask which is equipped with a condenser, a thermometer and a mechanical stirring. Since the lower critical solution temperature of NIPAM is 32℃, the flask was put into a water bath whose temperature was 40℃ (slightly higher than 32℃ to allow a sufficient contact of the reactants). After which CTS (0.9 g), GO dispersion (0.002 g/mL, 10 mL) and NIPAM (0.5 g) were put into the flask consecutively. The mixture was stirred vigorously at 40℃ for 30 min. The water bath was slowly warmed to 63℃, after which MBA solution (0.005 g/mL, 4 mL) and KPS solution (0.05 g/mL, 7 mL) was dropped into the flask consecutively under nitrogen atmosphere. This temperature is proper for the intercalation polymerization reaction without changing the properties of the product as a fact that the amount of NIPAM is much smaller compared with that of AA. Then the reaction mixture was allowed to react for about 1 h till a black gel formed. The gel was taken out, washed thoroughly with deionized water till the surface pH value is 7. Then it was cut into small pieces and dried in an oven at 60℃ to a constant weight. Solubility study showed that the gel is not soluble in common solvents such as water, ethanol, methanol and tetrahydrofuran. The synthetic process and the product are shown in Fig. 1.

2.3

2.3 Characterization

IR spectra were recorded using KBr tablet on a Nicolet's 380 Fourier transform infrared spectrometer (Nicolet Instrument Co., ltd., Switzerland). XRD spectrograms were performed on a Rigaku Corporation Ulti X-ray diffractometer (Japan Science Corporation), the scanning range was 5 to 60°, the speed was 8°/min, the current was 30 mA and the voltage was 40 kV. SEM photos were taken on a SU8000 scanning electron microscope. TGA curves were obtained on a TGA2 thermogravimetric analyzer (Mettler Toledo Company, Switzerland) using dry nitrogen purge, the heating rate was 10℃/min.

2.4

2.4 Adsorption tests

Dry CTS-g-P(AA-co-NIPAM) /GO powder (0.05 g) was put in a beaker with 150 mL of dye solutions at room temperature. After a certain period of time, the mixture was filtrated and the filtrate was retained for further determination of absorbency. The volume and the absorbency of the filtrate at the maximum absorption wavelength (λ^max) were measured. In consideration of the swelling ability of the composite hydrogel which leads to change of the volume of the dye solution, the equivalence adsorption capacity (q_e) was calculated on basis of Eq.(1),

(1)

q_{e} = \frac{C_{0} V_{0} - C_{t} V_{t}}{m}

where q_e (mg/g) is the equivalence adsorption capacity, C₀ and C_t (mg/L) are the concentrations of the dye solution before and after adsorption, respectively. V₀ and V_t (mL) are the volumes of the dye solution before and after adsorption, respectively. m (g) is the mass of the dry composite powder used for the adsorption of dyes.

3 Results and discussion

3.1

3.1 Characterization of the composite

The IR spectra of GO, CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM)/ GO are shown in Fig. 2a. It can be seen the broad stretching vibration peak of –OH from 3100 to 3500 cm⁻¹, C⚌O at 1727 cm⁻¹ and C⚌C at 1621 cm⁻¹ in GO. The peak at 1058 cm⁻¹ is the absorption of the sp3 hybridization carbon atom (C-OH) (Abdi et al., 2017). As for CTS-g-P(AA-co-NIPAM) graft copolymer, the broad peak around 3430 cm⁻¹ is ascribed to the overlapping stretching vibration of –OH in poly acrylic acid (PAA) and –NH₂ in poly N-isopropylacrylamide (PNIPAM). The peak at 2950 cm⁻¹ is due to the stretching vibration of C—H in the methane group of PNIPAM. That at 1586 cm⁻¹ is due to the bending vibration of N—H. The stretching vibration of C—N in chitosan is at 1402 cm⁻¹. Actually, there is no absorption peaks of C⚌C, meaning that the monomers have been grafted onto the backbone of CTS (Chen et al., 2016). When it comes to CTS-g-P(AA-co-NIPAM)/GO composite, the broad peak around 3430 cm⁻¹ is attributed to the stretching vibration of –OH and –NH₂. This peak is relatively broader than that in CTS-g-P(AA-co-NIPAM) graft copolymer due to the incorporation of GO. That at 1727 cm⁻¹ is resulted from the stretching vibration of C⚌O in both GO and poly AA-co-NIPAM side chain. The peak at 1600 cm⁻¹ comes from the stretching vibration of C⚌C in GO. Compared with that in GO, there is a blue shift in the wave number of C⚌C in the composite (from 1621to 1600 cm⁻¹) indicating the interactions between GO and CTS-g-P(AA-co-NIPAM) graft copolymer.

(a)IR spectroscopy; (b) XRD patterns; (c) SEM images; (d) TGA curves of GO, CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM)/GO.

Fig. 2b shows the XRD patterns of GO, CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM)/GO. As for GO there is a strong peak at 2θ = 12.04°. The corresponding slice distance is calculated to be 0.7351 nm according to the Bragg formula 2dsinθ = λ. For CTS-g-P(AA-co-NIPAM), there is no obvious diffraction peaks, indicating an amorphous state of the copolymer. When it comes to CTS-g-P(AA-co-NIPAM)/GO composite, the diffraction peak of GO totally disappears, indicating that GO have been peeled off and dispersed into CTS-g-P(AA-co-NIPAM) graft copolymer evenly (Didehban et al., 2017).

The SEM photos of GO, CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM)/GO are shown in Fig. 2c. It can be seen that GO is covered with irregular thin slices. Both CTS-g-P(AA-co-NIPAM) graft copolymer and CTS-g-P(AA-co-NIPAM)/GO composite are gel structures. The surface of CTS-g-P(AA-co-NIPAM) graft copolymer is loose and uneven. As for CTS-g-P(AA-co-NIPAM)/GO composite, there are plenty of holes and chinks with different sizes. Obviously, it is most convenient for small molecules to be adsorbed onto the surface of the composite.

The TGA curves of GO, CTS-g-P(AA-co-NIPAM) graft copolymer and CTS-g-P(AA-co-NIPAM)/GO composite are shown in Fig. 2d. As can be seen there are two weight loss stages in GO. The first stage is from 150 to 270℃ (weight loss 15.3 %), due to the evaporation of the adsorbed moisture. The second one is between 270 and 410℃ (weight loss 8.3 %), in which the oxygen-containing functional groups decomposed gradually. As for CTS-g-P(AA-co-NIPAM) graft copolymer and CTS-g-P(AA-co-NIPAM)/GO composite, they have similar weight loss stages. However, the weight loss is quite different. For CTS-g-P(AA-co-NIPAM), the first stage from 100 to 430 ℃ with a weight loss of 11.1 % is ascribed to the damage of the crosslinking networks. The second one from 450 to 630 ℃ with a weight loss of 8.8 % is due to the decomposition of the polymeric backbones. While for CTS-g-P(AA-co-NIPAM)/GO composite, the first stage is from 100 to 360℃ and the second one is from 480 to 650℃, the corresponding weight loss is 5.1 % and 7.3 %, respectively. At 800℃, the residue of CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM)/GO is 62.2 % and 73.3 %, respectively. Thus, despite the fact that GO exhibits lowest thermal stability of the three, the incorporation of GO actually brings about an improvement of the thermal stability of the composite. This indicates that the oxygen groups that are removed from the GO surface react with the functional groups of the copolymers (Chrissopoulou et al., 2021). In addition, the numerous hydrogen bonds between GO and CTS-g-P(AA-co-NIPAM) graft copolymer also helps to improve the thermal stability of the composite. (see Fig. 3c).

Formation mechanism of the composite. (a) structure of CTS-g-P(AA-co-NIPAM) graft copolymer; (b) network structure of CTS-g-P(AA-co-NIPAM) graft copolymer; (c) hydrogen bonds between GO and CTS-g-P(AA-co-NIPAM); (d) network structure of CTS-g-P(AA-co-NIPAM)/GO composite.

3.2

3.2 Formation mechanism of the composite

The formation mechanism of CTS-g-P(AA-co-NIPAM)/GO composite is shown in Fig. 3. AA and AIPAM monomers could be grafted onto glucose rings and form the network structure via free radical graft polymerization. The free radicals such as and SO₄^-⋅ and HO⋅ are produced with the decomposition of initiator KPS. Then CTS free radicals were generated by the initiation of SO₄^-⋅ and HO⋅. The graft copolymerization was proceeded by the reaction of the monomers (AA and NIPAM) and the CTS free radicals (Zhu et al., 2019). Meanwhile, GO and CTS-g-P(AA-co-NIPAM) are combined by hydrogen bonds (–OH⋅⋅⋅COOH, –COOH⋅⋅⋅COOH). The network structure of on adsorption /GO composite is shown in Fig. 3d.

3.3

3.3 Effect of different conditions on adsorption

3.3.1

3.3.1 Effect of GO content

The effect of GO content on adsorption is shown in Fig. 4a (adsorbent 0.05 g, dye concentration 1000 mg/L, time 24 h). It is clear that adsorption capacities increase first and then decrease with the growth of GO content. The adsorption capacities of MB and FB are 842.1 and 633.7 mg/g, respectively as the volume of GO suspension is zero. However, with 0.02 g (0.002 g/mL, 10 mL) of GO, adsorption of MB and FB grows sharply to 1496.3 and 1000.8 mg/g, respectively, as shown in Fig. 4b. The amount is 77.7 % and 57.9 %, respectively, higher than that onto CTS-g-P(AA-co-NIPAM) hydrogel produced under same conditions without GO. As a fact that GO combines with the functional groups on dye molecules by hydrogen bonds or electrostatic interactions （see Fig. 5a and Fig. 5c）as well as improve the network structure of the composite（Fig. 3d）, the adsorption capacities are improved greatly. In addition, with plenty of hydrophilic functional groups, GO also acts as adsorbent during the adsorption of dyes. However, if the content of GO exceeds 0.02 g, the excessive GO holds back the extension of the polymeric chains and the adsorption capacities decrease accordingly.

(a)Effect of content of GO on adsorption；(b) adsorption capacity on CTS-g-P(AA-co-NIPAM) and CTS-g-P(AA-co-NIPAM) /GO; (c) effect of initial concentration of dye solutions; (d) effect of contact time; (e) effect of adsorbent dosage; (f) effect of ionic strength on adsorption capacities; (g)effect of temperature on adsorption of MB; (h)effect of temperature on adsorption of GB.

(a) Interactions of CTS-g-P(AA-co-NIPAM), GO and methylene blue; (b) diagram of adsorption of MB onto the composite; (c) Interactions of CTS-g-P(AA-co-NIPAM), GO and fuchsine basic; (d) diagram of adsorption of FB onto the composite.

3.3.2

3.3.2 Effect of initial dye concentrations

The effect of initial dye concentration on adsorption is shown in Fig. 4c (adsorbent 0.05 g, GO 0.02 g, time 24 h). It can be seen that the adsorption capacities of both dyes increase rapidly as dye concentrations rise from 100 to 2000 mg/L and then approaches equilibria. Since there are a large number of negative charges on the composite but positive ones on dye molecules, the increase of dye concentrations is sure to strengthen the electrostatic interactions between the composite and dye molecules (see Fig. 5) (Liu et al., 2010). Finally, with the continuous growth of dye concentrations the adsorption capacities of MB and FB reaches equilibrium, which are 2748.1 and 2246.9 mg/g, respectively.

3.3.3

3.3.3 Effect of contact time

The effect of contact time on adsorption is shown in Fig. 4d (adsorbent 0.05 g, GO 0.02 g, dye concentration 1000 mg/L). It can be seen that the adsorption capacities of both dyes increase rapidly at the first 12 h (720 min) and then approach equilibria gradually. There are plenty of adsorption sites on the composite at the initial stages. However, after the adsorption sites are gradually covered with dye molecules, the adsorption of dyes approaches equilibrium. The equilibrium adsorption time is about 24 h (1440 min).

3.3.4

3.3.4 Effect of adsorbent dosage

The effect of the adsorbent dosage on adsorption is shown in Fig. 4e (time 24 h, dye concentration 1000 mg/L). The adsorption capacities of MB and FB decrease from 2389.1 and 1803.2 mg/g, respectively, to 383.7 and 278.4 mg/g, respectively, as the dosage of CTS-g-P(AA-co-NIPAM)/GO composite increases from 0.02 to 0.10 g. With further increase of the adsorbent dosage, the adsorption capacities hardly change. Therefore, batch delivery of adsorbents is more favorable in the industrial wastewater treatment.

3.3.5

3.3.5 Effect of ionic strength

The effect of ionic strength on adsorption is shown in Fig. 4f (adsorbent 0.05 g, GO 0.02 g, time 24 h, dye concentration 1000 mg/L). It is obvious that the adsorption capacities for both dyes first drop rapidly as the concentration of Na⁺ increases from 0 to 0.1 mol/L, and then keep constant with further increase of Na⁺ concentration. The competitive adsorption of Na⁺ on the composite is enhanced with the increase of Na⁺ at the initial stages. However, after the competitive adsorption approaches equilibrium the adsorption capacities change slightly with the growth of concentration of Na⁺.

3.3.6

3.3.6 Effect of temperature

Since poly N-isopropylacrylamide (PNIPAM) is a temperature sensitive hydrogel,the effect of temperature on adsorption of MB and FB is discussed, as shown in Fig. 4g and Fig. 4h, respectively (adsorbent 0.05 g, GO 0.02 g, dye concentration 1000 mg/L). It is clear that equilibrium adsorption capacities of both dyes increase with the rise of temperature. The thermal motion of dye molecules accelerates and the network of the gel expands at the same time as temperature rises, which make it easier for the dye molecules to contact with the adsorption sites on the composite. The good hydrophilicity caused by the hydrogen bonds between the amino and hydroxyl groups and water molecules presents the gel good swelling properties at lower temperatures (Zhang and Peppas, 2000). Although the hydrophobic property of PNIPAM gradually grows with the increase of temperature, which leads to a shrinkage of the polymeric chains, the effect on the adsorption capacity is not obvious because of the low proportion of NIPAM in the mixed monomers (AA 7.2 g, NIPAM 0.5 g, see the preparation part).

3.4

3.4 The adsorption isotherms

The adsorption isotherms are of great significance in studying the surface interactions between the adsorbent and adsorbate. The data of Fig. 4b are fitted according to the Langmuir (Eq.2), Freudlich (Eq.3) and Redlich-Peterson (Eq.4) equation, respectively. The calculated constants and correlation coefficients are shown in Table 2.

Table 2 the calculated constants and correlation coefficients for adsorption of MB and FB onto CTS-g-P(AA-co-AMPS)/GO composite hydrogel.

adsorption isotherm model			MB	FB
Langmuir	adsorption constant	q_m (mg/g)	4.640 × 10³	4.184 × 10³
	adsorption constant	K_l	4.728 × 10^-4	3.408 × 10^-4
	correlation coefficient	R²	0.9434	0.9288
Freundlish	adsorption constant	n	1.670	1.517
	adsorption constant	K_f	22.38	10.69
	correlation coefficient	R²	0.8849	0.8903
Redlich-Peterson	adsorption constant	A	1.519	1.073
		B	2.218 × 10^-10	1.359 × 10^-10
		g	2.709	2.735
	correlation coefficient	R²	0.9854	0.9556

Langmuir isotherm equation,

(2)

\frac{C_{e}}{q_{e}} = \frac{1}{q_{m} K_{l}} + \frac{C_{e}}{q_{m}}

where C_e is the equilibrium dye concentration (mg/L), q_e is the the equilibrium adsorption capacity (mg/g), q_m is the maximum adsorption capacity (mg/g), K_l is the Langmuir adsorption constant (L/mg).

Freundlish isotherm equation,

(3)

q_{e} = K_{f} C_{e}^{1 / n}

where q_e is the equilibrium adsorption capacity (mg/g), K_f and n are the empirical constants.

Redlich-Peterson (R-P) isotherm equation,

(4)

q_{e} = K C_{e} / (1 + α C_{e}^{β})

where q_e is the equilibrium adsorption capacity (mg/g), K and α are the constants, β is a coefficient ranged from 0 to 1.

It can be confirmed from the R² values that the adsorption of both MB and FB conform to the Redlich-Peterson equation. The adsorption is a monolayer one.

3.5

3.5 Adsorption thermodynamics

By substituting the values of K_f and n which are obtained from the Freundlish equation in Eq (5), the equilibrium constant K can be calculated. Furthermore, the Gibbs free energies are obtained by substituting the values of K, R (8.314 J/mol/K) and T (298.15 K) into Eq.(6). It is calculated that △G_FBθ = -4.6134KJ/mol < 0, and △G_MBθ = -3.8713KJ/mol < 0. Therefore, the adsorption of both FB and MB onto CTS-g-P(AA-co-AMPS)/GO are spontaneous.

(5)

K = {(K_{f})}^{1 / n}

(6)

Δ G^{θ} = - R T l n K

3.6

3.6 Adsorption kinetics

In order to study the adsorption kinetics, the data of Fig. 4c are fitted according to the pseudo-first-order (Eq.7) and pseudo-second-order (Eq.8) kinetic equation, respectively, and the results are shown in Table 3.

Table 3 The kinetic parameters for adsorption of MB and FB onto CTS-g-P(AA-co-NIPAM)/GO composite.

adsorption isotherm model		MB	FB
Pseudo first-orde	k₁(h⁻¹)	0.2645	0.3997
	q_e(mg·g⁻¹)	1.481 × 10³	1.358 × 10³
	R²	0.9538	0.8617
Pseudo second-order	k₂(g·mg⁻¹·h⁻¹)	1.435 × 10^-4	3.389 × 10^-4
	q_e(mg·g⁻¹)	1.783 × 10³	1.413 × 10³
	R²	0.9926	0.9637

Pseudo-first-order Equation,

(7)

\lg (q_{e} - q_{t}) = l g q_{e} - k_{1} t / 2.303

Pseudo-second-order Equation:

(8)

t / q_{t} = 1 / (k_{2} q_{e}^{2}) + t / q_{e}

where q_e is the equilibrium adsorption capacity (mg/g), q_t is the adsorption capacity (mg/g) at time t (min), k₁ (min⁻¹) and k₂ (g/mg/min) are the rate constants of Pseudo-first-order equation and Pseudo-second-order equation, respectively.

It can be inferred from the R² values in Tab.3 that the adsorption of both dyes conform to the Pseudo second-order equation, chemical adsorption is the rate-determining step (Chen et al., 2009).

3.7

3.7 Adsorption mechanisms

The interactions between CTS-g-P(AA-co-NIPAM)/GO composite and MB and FB are shown in Fig. 5a and Fig. 5c, respectively. As for MB, the interaction is electrostatic attraction. While for FB, there are hydrogen bonds as well as electrostatic attraction. The diagrams of adsorption of MB and FB on the composite are shown in Fig. 5b and Fig. 5d, respectively.

3.8

3.8 Comparison with other adsorbents

The comparison of the equilibrium adsorption capacities of MB and FB onto CTS-g-P(AA-co-NIPAM/GO composite hydrogel with other adsorbents is shown in Table 4. It is obvious that the present composite hydrogel exhibits remarkable adsorption properties.

Table 4 Comparison of the composite hydrogel with other adsorbents.

Adsorbent/capacity	MB(mg/g)	FB(mg/g)	references
CTS-g-P(AA-co-NIPAM/GO	2748.1	2246.9	present study
GBC-120	1050	—	(Narvekar et al., 2018)
nGO-(NH)R	977.06	—	(Fraga et al., 2020)
agar-GO	79.51	38.11	(de Araujo et al., 2022)
GO	504	—	(de Araujo et al., 2018)

3.9

3.9 Recycling of the composite hydrogel

The swollen composite hydrogels which has been immersed in the dye solutions (1000 mg/L) for 24 h was taken out and put in a beaker with 100 mL of 5 % hydrochloric acid to undergo desorption. After staying in the HCl solution for 12 h, the gel was taken out, dried and ground to adsorb the dye solutions (1000 mg/L) again. The recycling property of the gel was shown in Fig. 6. It can be seen that the adsorption capacities of MB and FB are 488.6 and 496.7 mg/g, respectively after four times of sorption and desorption experiment. Thus, the composite hydrogel has good reuse performances in wastewater treatment.

the reuse performances of (CTS-g-P(AA-co-NIPAM/GO) composite.

4 Conclusions

In this article, chitosan graft poly (acrylic acid-co-N-isopropylacrylamide) /graphite oxide (CTS-g-P(AA-co-NIPAM/GO) composite hydrogel is synthesized and characterized. The composite is used to remove methylene blue (MB) and fuchsine basic (FB) from aqueous solutions by adsorption. The effect of the adsorption conditions, including the content of graphite oxide (GO), the initial concentration of dye solutions, contact time, dosage of the composite and ionic strength, on the adsorption capacities has been studied. It is found that the growth rate in terms of adsorption capacities of MB and FB are 77.7 %（from 842.1 to 1496.3 mg/g）and 57.9 % (from 633.7 to 1000.8 mg/g), respectively, with an incorporation of 0.02 g of GO. The interactions of the CTS-g-P(AA-co-NIPAM)/GO composite and MB is electrostatic attraction, while those of FB is electrostatic attraction as well as hydrogen bonds.

The adsorption of both MB and FB on CTS-g-P(AA-co-NIPAM/GO are spontaneous and satisfies the Redlich-Peterson equation. Kinetics study show that the adsorption of both dyes is in accordance with the Pseudo second-order kinetic model. The composite has good reuse performances in wastewater treatment.

Funding

This work is supported by the Project of Shandong Province Higher Educational Science and Technology Program (J13LD07).

6 Author's contribution

Kyohairwe Angela Mwesigye, Bin Zhou and Fangyuan Wang completed the experimental part. Linhui Zhu and Yaoji Tang wrote the main manuscript text and prepared the figures. All authors reviewed the manuscript.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Show Sections

[1] Abdi J., Vossoughi M., Mahmoodi N.M., Alemzadeh I., . Synthesis of metal-organic framework hybrid nanocomposites based on GO and CNT with high adsorption capacity for dye removal. Chem. Eng. J.. 2017;326:1145-1158.
[CrossRef] [Google Scholar]

[2] Abu-Nada A., Abdala A., McKay G., . Removal of phenols and dyes from aqueous solutions using graphene and graphene composite adsorption: a review. J. Environ. Chem. Eng.. 2021;9:105858
[CrossRef] [Google Scholar]

[3] Badawi A.K., Elkodousb M.A., Ali G.A.M., . Recent advances in dye and metal ion removal using efficient adsorbents and novel nano-basedmaterials: an overview. RSC Adv.. 2021;11:36528-36553.
[CrossRef] [Google Scholar]

[4] Boddu V.M., Naismith N.K., Patel H.R., . Environmentally responsive Poly(N-isopropylacrylamide)-co-poly(acrylic acid) hydrogels for separation of toxic metals and organic explosive compounds from water. J. Polym. Environ.. 2019;27:571-580.
[CrossRef] [Google Scholar]

[5] Calimli M.H., Nas M.S., Buran H., Mustafov S.D., Demirbas O., Sen F., . Preparation, characterization and adsorption kinetics of methylene blue dye in reduced-graphene oxide supported nanoadsorbents. J. Mol. Liq.. 2020;309:113171
[CrossRef] [Google Scholar]

[6] Chen J., Gao L., Han X., Chen T., Luo J., Liu K., Gao Z., Zhang W., . Preparation and electro-response of chitosan-g-poly (acrylic acid) hydrogel elastomers with interpenetrating network. Mater. Chem. Phys.. 2016;169:105-112.
[CrossRef] [Google Scholar]

[7] Chen S., Shen W., Yu F., Wang H., . Kinetic and thermodynamic studies of adsorption of Cu²⁺ and Pb²⁺ onto amidoximated bacterial cellulose. Polym. Bull.. 2009;63:283-297.
[CrossRef] [Google Scholar]

[8] Choi H.J., . Effect of Mg-sericite flocculant for treatment of brewery wastewater. Appl. Clay Sci.. 2015;115:145-149.
[CrossRef] [Google Scholar]

[9] Chrissopoulou K., Androulaki K., Labardi M., Anastasiadis S.H., . Static and dynamic behavior of polymer/graphite oxide nanocomposites before and after thermal reduction. Polymers. 2021;13:1008.
[CrossRef] [Google Scholar]

[10] Crini G., . Wastewater treatment by sorption. In: Crini G., Badot P.M., eds. Sorption Processes and Pollution, Chap 2. Besançon: PUFC; 2010. p. :39-78.
[Google Scholar]

[11] Crini G., Lichtfouse E., Wilson L., Morin-Crini N., . Conventional and non-conventional adsorbents for wastewater treatment. Environ. Chem. Lett.. 2019;17(1):195-213.
[CrossRef] [Google Scholar]

[12] da Silva L.H.B.R., Paixao R.M., Bergamasco R., Vieira A.M.S., Vieira M.F., . Layer-by-layer self-assembly of polyethersulphone microfiltration membranes for dye removal and flux recovery improvement. Can. J. Chem. Eng.. 2021;100:1920-1929.
[CrossRef] [Google Scholar]

[13] Dadfarnia S., Haji Shabani A.M., Moradi S.E., Emami S., . Methyl red removal from water by iron based metal-organic frameworks loaded onto iron oxide nanoparticle adsorbent. Appl. Surf. Sci.. 2015;330:85-93.
[CrossRef] [Google Scholar]

[14] Damodar R.A., You S.J., Ou S.H., . Coupling of membrane separation with photocatalytic slurry reactor for advanced dye wastewater treatment. Sep. Purif. Technol.. 2010;76:64-71.
[CrossRef] [Google Scholar]

[15] de Araujo, C.M.B., de Assis Filho, R.B., Baptisttella, A.M.S., do Nascimento, G.F.O., da Costa, G.R.B., Carvalho, M.N., Ghislandi, M.G., da Motta Sobrinho, M.A., 2018. Systematic study of graphene oxide production using factorial design techniques and its application to the adsorptive removal of methylene blue dye in aqueous medium. Mater. Res. Express, 5, 065042. https://doi.org/10.1088/2053-1591/aacb51

[16] de Araujo, C.M. B., Ghislandi, M.G., Rios, A.G., da Costa, G.R.B., do Nascimento, B.F., Ferreira, A.F.P., da Motta Sobrinho, M.A., Rodrigues A.E., 2022.Wastewater treatment using recyclable agar-graphene oxide biocomposite hydrogel in batch and fixed-bed adsorption column: bench experiments and modeling for the selective removal of organics. Colloid Surface A, 649, 128357. https://doi.org/10.1016/j.colsurfa.2022.128357

[17] Didehban K.H., Mohammadi L., Azimv J., . Preparation of RGO/Fe₃O₄/poly (acrylic acid) hydrogel nanocomposites with improved magnetic, thermal and electrochemical properties. Mater. Chem. Phys.. 2017;195:162-169.
[CrossRef] [Google Scholar]

[18] Fallah S., Mamaghani H.R., Yegani R., Hajinajaf N., Pourabbas B., . Use of graphene substrates for wastewater treatment of textile industries. Adv. Compos Hybrid. Ma.. 2020;3:187-193.
[CrossRef] [Google Scholar]

[19] Fraga T.J.M., de Souza Z.S.B., dos Marques Fraga D.M., Carvalho M.N., de Luna Freire E.M.P., Ghislandi M.G., da Motta Sobrinho M.A., . Comparative approach towards the adsorption of Reactive Black 5 and methylene blue by n-layer graphene oxide and its amino-functionalized derivative. Adsorption. 2020;26:283-301.
[CrossRef] [Google Scholar]

[20] Fu, C.L., Dong, X.B., Wang, S.J., Kong, F.G., 2019. Synthesis of nanocomposites using xylan and graphite oxide for remediation of cationic dyes in aqueous solutions, 137, 886-894. https://doi.org/10.1016/j.ijbiomac.2019.07.037

[21] Gupta V.K., Saleh T.A., . Sorption of pollutants by porous carbon, carbon nanotubes and fullerene- an overview. Environ. Sci. Pollu. Res.. 2013;20:2828-2843.
[CrossRef] [Google Scholar]

[22] Gupta V.K., Mittal A., Gajbe V., Mittal J., . Adsorption of basic fuchsin using waste materials-bottom ash and deoiled soya-as adsorbents. J. Colloid Interf. Sci.. 2008;319:30-39.
[CrossRef] [Google Scholar]

[23] Hermann A., Mruk R., Roskamp R.F., Scherer M., Ma L.Q., Zentel R., . Poly(N-isopropylacrylamide)-modified syrene-butadiene rubber as thermoresponsive material. Macromol. Chem. Phys.. 2014;215:32-43.
[CrossRef] [Google Scholar]

[24] Hummers W., Offema R., . Preparation of graphitic oxide. J. Am. Chem. Soc.. 1958;80:1339.
[CrossRef] [Google Scholar]

[25] Ifuku S., Miwa T., Morimoto M., Saimoto H., . Thermoresponsive chitosan/N-isopropylacrylamide copolymer through atom transfer radical polymerization. Int. J. Biol. Macromol.. 2013;52:14-19.
[CrossRef] [Google Scholar]

[26] Iqbal A., Cevik E., Bozkurt A., Asiri S.M.M., Alagha O., Qahtan T.F., Jalees M.I., Farooq M.U., . Ultrahigh adsorption by regenerable iron-cobalt core-shell nanospheres and their synergetic effect on nanohybrid membranes for removal of malachite green dye. J. Environ. Chem. Eng.. 2022;10:107968
[CrossRef] [Google Scholar]

[27] Jana, S., Ray, J., Mondal, B., Tripathy, T., 2019. Efficient and selective removal of cationic organic dyes from their aqueous solutions by a nanocomposite hydrogel, katira gum-cl-poly(acrylic acid-co-N, N-dimethylacrylamide) @bentonite, 173,46-64. https://doi.org/10.1016/j.clay.2019.03.009.

[28] Kametani Y., Sawamoto M., Ouchi M., . Control of the alternating sequence for n-isopropylacrylamide (NIPAM) and methacrylic acid units in a copolymer by cyclopolymerization and transformation of the cyclopendant group. Angew. Chem. Int. Edit.. 2018;57:10905-10909.
[CrossRef] [Google Scholar]

[29] Kozhunova E.Y., Komarova G.A., Vyshivannaya O.V., Nasimova I.R., Kuvarina A.E., Sadykova V.S., . Antiseptic materials on the base of polymer interpenetrating networks microgels and benzalkonium chloride. Int. J. Mol. Sci.. 2022;23:4394.
[CrossRef] [Google Scholar]

[30] Kumar R., Sharma R.K., Singh A.P., . Grafting of cellulose with N-isopropylacrylamide and glycidyl methacrylate for efficient removal of Ni(II), Cu(II) and Pd(II) ions from aqueous solution. Sep. Purif. Technol.. 2019;219:249-259.
[CrossRef] [Google Scholar]

[31] Liu M., Wen Y., Song X., Zhu J.L., Li J., . A smart thermoresponsive adsorption system for efficient copper ion removal based on alginate-g-poly(N-isopropylacrylamide) graft copolymer. Carbohyd. Polym.. 2019;219:280-289.
[CrossRef] [Google Scholar]

[32] Liu Y., Zheng Y., Wang A.Q., . Enhanced adsorption of Methylene Blue from aqueous solution by chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites. J. Environ. Sci.. 2010;22:486-493.
[CrossRef] [Google Scholar]

[33] Luna L.G., . Manual of Histologic Staining Methods of the AFIP ((3rd ed.),). New York: McGraw–Hill Book Company; 1968. p. :222.

[34] Ma H., Zhang H.X., Cao J.D., Tong M.Q., Zhao J.W., Li Y.F., Xu H., Wu W., . Temperature-responsive and piezoresistive performances of poly(N-isopropylacrylamide)-grafted reduced graphene oxide smart fiber. Compo. Sci. Technol.. 2019;169:186-194.
[CrossRef] [Google Scholar]

[35] Martinez-Moro M., Jenczyk J., Giussi J.M., Jurga S., Moya S.E., . Kinetics of the thermal response of poly(N-isopropylacrylamide co methacrylic acid) hydrogel microparticles under different environmental stimuli: a time-lapse NMR study. J. Colloid Interf. Sci.. 2020;580:439-448.
[CrossRef] [Google Scholar]

[36] Narvekar A.A., Fernandes J.B., Tilve S.G., . Adsorption behavior of methylene blue on glycerol based carbon materials. J. Environ. Chem. Eng.. 2018;6:1714-1725.
[CrossRef] [Google Scholar]

[37] Pandey A., Singh P., Iyengar L., . Bacterial decolorization and degradation of azo dyes. Int. Biodeterior. Biodegrad.. 2007;59:73-84.
[CrossRef] [Google Scholar]

[38] Parasuraman D., Sarker A.K., Serpe M.J., . Recyclability of poly (N-isopropylacrylamide) microgel-based assemblies for organic dye removal from water. Colloid Polym. Sci.. 2013;291:1795-1802.
[CrossRef] [Google Scholar]

[39] Saravanan R., Sacari E., Gracia F., Khan M.M., Mosquer E., Gupta V.K., . Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes. J. Mol. Liq.. 2016;221:1029-1033.
[CrossRef] [Google Scholar]

[40] Siciliano A., Curcio G.M., Limonti C., Masi S., Greco M., . Methylene blue adsorption on thermo plasma expanded graphite in a multilayer column system. J. Environ. Manage.. 2021;296:113365
[CrossRef] [Google Scholar]

[41] Soleimani F., Sadeghi H., Shahsavari H., Soleimani A., Sadeghi F., . Studies of swelling kinetics of carboxymethyl cellulose-g-PMAAm-co-PNIPAm superabsorbent hydrogels. Asian J. Chem.. 2013;25:4851-4855.
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substance	methylene blue (MB)	fuchsin basic(FB)
molecular formula	C₁₆H₁₈ClN₃S	C₂₀H₂₀ClN₃
molecular Weight	319.85	337.85
λ^max (nm)	664	543
appearance	dark green powder/crystal	green crystal
chemical structure three dimensional structure

Novel dye removing agent based on CTS-g-P(AA-co-NIPAM)/GO composite

Abstract

Keywords

Graphite oxide

Composite

Adsorption

Dyes

1 Introduction

2 Experimental

2.1 Materials

2.2 Preparation

2.2.1 Preparation of GO

2.2.2 Preparation of CTS-g-P(AA-co-NIPAM) /GO

2.3 Characterization

2.4 Adsorption tests

3 Results and discussion

3.1 Characterization of the composite

3.2 Formation mechanism of the composite

3.3 Effect of different conditions on adsorption

3.3.1 Effect of GO content

3.3.2 Effect of initial dye concentrations

3.3.3 Effect of contact time

3.3.4 Effect of adsorbent dosage

3.3.5 Effect of ionic strength

3.3.6 Effect of temperature

3.4 The adsorption isotherms

3.5 Adsorption thermodynamics

3.6 Adsorption kinetics

3.7 Adsorption mechanisms

3.8 Comparison with other adsorbents

3.9 Recycling of the composite hydrogel

4 Conclusions

Funding

6 Author's contribution

Declaration of Competing Interest

References

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